The goal of this project is to determine the mechanisms behind Human cytomegalovirus (HCMV) accelerated transplant vascular sclerosis (TVS) and chronic rejection (CR) of solid organ grafts. Approximately 75% of the solid organ donor/recipient population is infected with HCMV making it difficult to avoid the effects of HCMV. During clinical latency, CMV infections cause extraordinary immune responses that are associated with a number of CMV-induced inflammatory diseases including solid organ transplant CR. The mechanisms involved in promoting these deleterious immune responses during latency are still unknown, although they could be mediated by either the anti-viral response to latent virus or by viral genes expressed during persistence that actively promote immune cell infiltration, or both. To determine the mechanisms of immune infiltration and its effects on CR, we have developed a rat heart transplant CR model that exhibits the hallmarks of TVS/CR in humans. Rat CMV (RCMV) infection significantly accelerates the development of TVS/CR in heart allografts from latently infected donors. Surprisingly, ganciclovir treatment of recipients of latently infected donor hearts does not prevent TVS/CR, as its treatment does in acutely infected recipients. We have discovered the accumulation of activated T cells and macrophages in CMV-latently infected hearts prior to transplantation. Passenger leukocytes have been associated with CR and we hypothesize that RCMV-induced alteration of donor tissue immune profiles prior to transplantation mediates the ganciclovir-insensitive rejection of latently infected donor tissues in nave recipients by providing a scaffold for immune activation. We have found that the RCMV encoded chemokines R129 and R131 (homologues of HCMV UL128 and UL130) are chemotactic towards rat lymphocytes. We hypothesize that these virus-encoded chemokines mediate immune cell infiltration into the heart during latency and predispose the allograft for accelerated CR. However, R129 and R131 are also part of the gH/gL entry complex required for infection of endothelial cells and macrophages. The focus of our proposal is to determine how R129 and R131 mediate immune cell migration and rejection by dissecting the two proposed functions of these molecules using in vitro assays and in vivo pathogenesis and transplantation models. In SA1, we will make point mutations in R129 and R131 that separate chemokine activity from entry mechanisms and test them using migration, ligand binding and entry assays. These mutations will be incorporated into RCMV using BAC recombineering and the viruses will be used in SA2 to characterize the immune cells that infiltrate the heart during latency and promote lymphoid structure formation. We will characterize the changes in T cell profiles in donor hearts during latency as well as their CMV specificity and determine whether chemokine vs. entry complex activity is required for these processes. In SA3, we will determine the role that the viral chemokines play in promoting rejection of latently infected donor hearts by transplanting infected hearts harboring viruses with chemokine vs. entry defects.